The present invention relates to a tire and rim assembly capable of running safely without allowing tire beads to be dislocated from the wheel rim under such conditions where the internal pressure of the tire is lowered or that the vehicle makes a sharp turn at high speed. The present invention is also directed to a tire capable of being used in the assembly and also capable of being mounted on a standard rim.
In conventional tire and rim assemblies, the beads of the tire are retained on the rim bases of the rim by means of the friction force therebetween due to the internal pressure of the tire. Accordingly, when the internal pressure of the tire is lowered, the retaining force is also reduced, and if a cornering operation is made in a state where the internal pressure is greatly lowered by puncture, then the beads are removed from the wheel rim by the accompanying lateral force. Especially when the rim is provided with a well for tire mounting work, the beads fall into the well, and as a result, the tire is completely seperated from the rim, and a serious accident is induced.
The lateral force caused by cornering shifts the tread in the lateral direction, and this shift is transferred to the beads through the sidewalls, and the bead is subjected to a force F in the axial direction and also a moment M around a bead core, for example as shown in FIG. 5, which is, however, a figure showing the operation of the tire and rim assembly according to the present invention. Under such condition, if the internal pressure of the tire is low, the moment lifts up the heel of the bead to reduce the friction force with the rim, and the bead is moved axially inwardly on the tapered rim base RB, which lowers the tension of the bead core, and as a result, the retaining force of the bead is suddenly decreased, and finally the bead falls into the well WE.
To solve the above-mentioned problems, there have been proposed:
the use of a rim without a well;
the use of a rim provided at the axially inner edge of the rim base with a hump on which the toe of the bead impinges;
the combination use of a rim provided with a hump in the range of the rim base and a tire provided with an annular groove to engage with the hump (Japanese Patent Application KOKAI No. 49-13802); and
the combination use of a rim provided at the axially inner edge of the rim base with an annular groove and a tire provided at the bead toe with a protubarance to be inserted with the annular groove (Japanese Patent Publication TOKKYO KOHO No. 57-15007). However, the rim disclosed in the Japanese Patent Publication TOKKYO KOHO No. 57-15007, is formed in a special shape so that it becomes impossible to use with conventional standard tires.
Further, in International Publication No. WO87/06889, there has been proposed a tire and rim assembly and a rim capable of keeping the bead safe at low internal pressure in which conventional standard tires can be used in addition to special tires designed therefor.
This assembly has superior effects as a bead retaining mechanism and the rim can be safely used with a standard tire having a conventional bead construction.
In such a special tire, however, there is the possibility that the beads are damaged if mounted on or demounted from the rim, and a little more labor is required for the mounting and demounting operation in comparison with the conventional tire and rim assembly. Moreover, if the special tire is mounted on a conventional standard rim, insufficient matching, that is, bead unseating may be caused due to the bead toe having a large volume.